Great diversification of passive income. I’m holding off on adding to passive income streams right now because I’ve still got a full time job and am already paying more than enough in taxes. It seems like a good strategy to focus on mortgage pay down and capital improvements to my existing rental property, and buying more growth stocks, then wait until after retirement or semiretirement to move things around with the goal of generating more passive income.
Additional income not only provides peace of mind, but it also means you need less money to retire on.  If your side business provides you $3000 a month, and you need $7000 a month to live on in retirement, you may be able to retire 5 or 10 years earlier than you otherwise might.  Instead of a $2.1 Million portfolio, you may only need $1.2 Million.  This, of course, assumes you’re willing to keep running the side business.
Residual income is the amount of net income generated in excess of the minimum rate of return. Residual income concepts have been used in a number of contexts, including as a measurement of internal corporate performance whereby a company's management team evaluates the return generated relative to the company's minimum required return. Alternatively, in personal finance, residual income is the level of income that an individual has after the deduction of all personal debts and expenses have been paid.